The present invention relates to a four wheel drive power transmission system, and more particularly relates to such a four wheel drive power transmission system for a vehicle such as an automobile adapted for four wheel drive operation, in which the construction is improved so as to eliminate the provision of universal joints for a front propeller shaft incorporated therein, thereby to minimize noise and vibration and maximize transmission working life.
The present invention has been described in Japanese Patent Application Ser. No. 60-195282 (1985), filed by an applicant the same as the entity assigned or owed duty of assignment of the present patent application; and the present patent application hereby incorporates into itself by reference the text of said Japanese Patent Application and the claims and the drawings thereof; a copy is appended to the present application.
Further, the present inventors wish hereby to attract the attention of the examining authorities to their copending Patent Applications Ser. Nos. 903,243 and 903,239, which may be considered to be material to the examination of the present patent application, and which are coowned with or are subject to obligations of coassignment together with the present patent application.
In Japanese Utility Model Application Laying Open Publication Ser. No. 47-203 (1972), as well as in the publication Ser. No. 710,615 of the Society of Automotive Engineers (SAE), neither of which is it intended hereby to admit as prior art to the present patent application except to the extent in any case required by applicable law, there is disclosed a four wheel drive power transmission system, comprising, connected in order to a power unit such as for example a front mounted longitudinally disposed internal combustion engine, in the specified order, a speed change device (i.e., a gearbox or automatic transmission or the like) and a power distribution device for four wheel drive operation (a so called transfer device) having a front wheel drive output shaft and a rear wheel drive output shaft, with one end each of a front propeller shaft and a rear propeller shaft being connected respectively to said front wheel drive output shaft and to said rear wheel drive output shaft, and with the other ends of said front propeller shaft and said rear propeller shaft being respectively connected to respective input shafts of power distribution devices such as speed reducing differential devices for respectively the front wheels of the vehicle and the rear wheels of the vehicle; with, particularly, the power distribution device for the front wheels of the vehicle being attached and mounted to an oil pan of the internal combustion engine; and, further, with a front universal joint being provided between the input shaft of said power distribution device for the front wheels and the front end of the front propeller shaft drivingly connected thereto, and also a rear universal joint being provided between said front wheel drive output shaft of said power distribution device for four wheel drive and the rear end of said front propeller shaft which is connected thereto and is driven thereby.
In a thus constructed four wheel drive power transmission system, the front propeller shaft is disposed on and passes along one side of the series coupled combination of the internal combustion engine, the speed change device, and the power distribution device for four wheel drive operation, and along the same direction along which said three units are coupled in series; and, as mentioned above, conventionally the front end of said front propeller shaft is connected to the end of said input shaft of said power distribution device for the front wheels (hereinafter referred to as the front differential device) by means of a universal joint, and also the rear end of said front propeller shaft is connected to the front wheel drive output shaft of the power distribution device for four wheel drive by another universal joint. This is done because the central longitudinal axis of the aforesaid combination of the internal combustion engine, the speed change device, and the power distribution device for four wheel drive operation, which typically is the axial line of said front wheel drive output shaft of said power distribution device for four wheel drive and also of said input shaft of said front differential device, is not generally parallel with the line of said front propeller shaft, and hence said two such universal joints are inevitably conventionally required to be provided. However, the problem arises that the front such a universal joint tends to fall, in its longitudinal positioning, just by the joining portion between the internal combustion engine and the speed change device, which typically is the portion of the combination of the aforementioned three units coupled in series which projects most to the side, especially in the case that the speed change device is an automatic transmission in which case said automatic transmission typically includes a torque converter which is very fat and bulky and causes a bulge in the housing receiving it. In order to avoid interference between the front universal joint and the joining portion between the internal combustion engine and the speed change device, the installation position of said front universal joint must be considerably spaced apart from said joining portion, i.e. must be located at a substantial distance from the conjoined combination of the internal combustion engine and the speed change device, and this not only increases the space taken up by the four wheel drive power transmission system, but also creates the requirement that the central axial line of the front propeller shaft must be angled at a considerable angle from the longitudinal axis of the conjoined combination of the internal combustion engine and the speed change device, which means that the joint angles of the aforementioned front and rear universal joints are increased. This can lead to problems with noise and vibration during four wheel drive operation and during rotation of the front propeller shaft, as well as to shortened service life and unsatisfactory reliability. Further, disadvantages arise from the point of view of mass production, because of the requirement for the front propeller shaft, the universal joints, and the front differential device to be each manufactured and fitted in place with a high degree of accuracy, in order to avoid the danger of the occurrence of incorrect assembly.